Where are you located?
I generally brake form the channels whenever making floor ribs.
In many cases, the boat manufacturer is going to have proprietary dies for their particular hat section. That means they have absolute rights to that die, so no one else could get a run of that shape without investing in new dies. And, being boat manufacturers, and not aluminum distributors, it isn't worth their time to sell specialty shapes, so finding replacements is tough.
That being said, there are 'some' available hat sections. I've seen them, in very small quantities, as the demand is next to nothing, in the stock at your 'average' steel distributor/retailer in coastal Alaska. That being said, back on this side of the country, I haven't been able to find a distributor (or retailer, for that matter), that has access to that shape.
Your best bet is to find someone to brake them out of sheet. I would recommend making the channel quite a bit wider than the original, unless you know the shops capability. To get the common 1.5 wide by 1.5 tall, the shop will need gooseneck punches on their press brake, and for some reason, a lot of shops don't own those, or you'd be paying a higher amount for a tooling change, as they don't keep the gooseneck punch on the machine for day to day operation.
By making the width wider (say 3-4"), any shop with a press brake can bend them with conventional punches, and your common 8 way lower die. Furthermore, you are only making the rib stronger than what was there originally.
Hope this helps.